Vitrified magnesia dissolution and its impact on plutonium residue processing

Aqueous chloride operations at the Los Alamos Plutonium Facility cannot directly dispose of acidic waste solutions because of compatibility problems with existing disposal lines. Consequently, all hydrochloric acid must be neutralized and filtered prior to exiting the facility. From a waste minimization standpoint, the use of spent magnesia pyrochemical crucibles as the acid neutralization agent is attractive since this process would take a stream destined for transuranic waste and use it as a reagent in routine plutonium residue processing. Since Los Alamos National Laboratory has several years of experience using magnesium hydroxide as a neutralizing agent for waste acid from plutonium processing activities, the use of spent magnesia pyrochemical crucibles appeared to be an attractive extension of this activity. In order to be competitive with magnesium hydroxide, however, size reduction of crucible shards had to be performed effectively within the constraints of glovebox operations, and acid neutralization time using crucible shards had to be comparable to neutralization times observed when using reagent-grade magnesium hydroxide. The study utilized non-plutonium-contaminated crucibles for equipment evaluation and selection and used nonradioactive acid solutions for completing the neutralization experiments. This paper discusses experience in defining appropriate size reduction equipment and presents results from using the magnesia crucibles for hydrochloric acid neutralization, a logical precursor to introduction into glovebox enclosures

Pyrochemical investigations into recovering plutonium from americium extraction salt residues

Progress into developing a pyrochemical technique for separating and recovering plutonium from spent americium extraction waste salts has concentrated on selective chemical reduction with lanthanum metal and calcium metal and on the solvent extraction of americium with calcium metal. Both techniques are effective for recovering plutonium from the waste salt, although neither appears suitable as a separation technique for recycling a plutonium stream back to mainline purification processes. 17 refs., 13 figs., 2 tabs

The Duration of Zidovudine Benefit in Persons With Asymptomatic HIV Infection: Prolonged Evaluation of Protocol 019 of the AIDS Clinical Trials Group

Objective.—To determine the durability of zidovudine-induced delay in clinical progression of asymptomatic human immunodeficiency virus (HIV) disease and to assess the relationship between this effect and the entry CD4+ cell count.Design and Interventions.—Extended follow-up data from subjects participating in protocol 019 of the AIDS [acquired immunodeficiency syndrome] Clinical Trials Group were examined. Subjects were offered a total daily dose of 500 mg of open-label zidovudine after the unblinding of the original randomized trial in 1989. Original treatment groups included placebo, 500 mg of zidovudine, or 1500 mg of zidovudine daily in divided doses. Three distinct analyses were conducted to assess the duration of zidovudine's effect on progression to AIDS or death: (1) analysis of all follow-up information from all subjects, (2) analysis of all subjects but with follow-up of original placebo-assigned subjects censored at the time open-label zidovudine was initiated, and (3) analysis of the effect of initiating zidovudine in subjects initially assigned to receive placebo.Setting.—University-based and university-affiliated AIDS research clinics participating in AIDS Clinical Trials Group protocol 019.Patients.—A total of 1565 asymptomatic HIV-infected subjects with entry CD4+ cell counts less than 0.50×109/L (500/μL).Main Outcome Measure.—Time to progression to AIDS or death.Results.—During follow-up of up to 4.5 years (mean, 2.6 years), 232 subjects progressed to AIDS or died. In each of the three analyses described herein, zidovudine was associated with a significant (P=.008,.004,.007) decrease in the risk of such progression. However, each of these analyses also indicated a decreasing placebo:zidovudine relative risk with duration of use (P=.002,.08,.04), suggesting a nonpermanent effect. The duration of benefit appeared to be related to entry CD4+ cell count, with greater benefit in those with higher counts at entry. No significant differences in survival were found between those originally randomized to zidovudine or placebo.Conclusions.—Zidovudine at 500 mg/d caused a significant delay in progression to AIDS or death, but its earlier use in asymptomatic disease was not associated with an additional prolongation of survival compared with delayed initiation. The delay in progression diminished over time especially in subjects with entry CD4+ cell counts less than 0.30×109/L (300/μL). Treatment strategies that alter drug regimens before the loss of zidovudine benefit should be explored.(JAMA. 1994;272:437-442